1. Field of the Invention
Embodiments of the invention generally relate to plasma processing systems and materials and apparatus for controlling plasma uniformity in plasma processing systems.
2. Description of the Related Art
Plasma processing chambers are regularly utilized in various electronic device fabrication processes, such as etching processes, chemical vapor deposition (CVD) processes, and other processes related to the manufacture of electronic devices on substrates. Many ways have been employed to generate and/or control the plasma density, shape, and electrical characteristics in processing chambers, such as capacitively or inductively coupled RF sources commonly used in conventional plasma chambers. For example, during a plasma assisted chemical vapor deposition process, processing gases are introduced into a processing chamber through a capacitively coupled showerhead that is disposed over a semiconductor substrate that is circumscribed by a process kit. Once a plasma is formed in a PECVD chamber, the plasma and process gas(es) interact with the substrate to deposit a desired material layer thereon.
Conventional plasma processing chamber designs in which the generated plasma is disposed over the substrate surface can cause unwanted sputtering and damage to the substrate surface due to the interaction of electrons and ions formed in the plasma with the substrate surface. Floating and electrically grounded components that are exposed to the generated plasma will generally accumulate a net charge. The formed net charge causes electrons and/or ions formed in the plasma to bombard and possibly damage the exposed surfaces of the substrate or chamber component. Thus, in some applications it is desirable to form gas radicals that have sufficient energy to easily react with the substrate surface, or surface of the chamber component, to enhance the reaction rate, while not energetically bombarding the surface of the substrate or chamber component, since the non-ionized gas radical is not affected by charge formed on the substrate or component surface.
Therefore, to prevent or minimize the plasma interaction with the substrate and chamber components, remote plasma source (RPS) designs have been used. Typical remote plasma source designs include a plasma generation region that is remotely positioned from the processing region of the processing chamber in which a substrate is positioned. In this way the plasma generated in the plasma generation region of the RPS device will generally not interact with the substrate surface.
However, current conventional RPS designs typically utilize microwave, capacitively coupled or inductively coupled energy sources that have a narrow plasma generating region, which will cause these devices to have a smaller than desirable plasma processing window that limits the range of energies of the formed gas radicals and gas ion that are formed in the plasma generating region of the conventional RPS device. In one example, as shown in FIG. 1, which is FIG. 3 in the issued U.S. Pat. No. 6,150,628, a conventional RPS design will generally include region 112, 114 of a metallic plasma chamber 100 in which a plasma is generated by the delivery of energy to a first and a second core 104, 106. One skilled in the art will appreciate that the electromagnetic energy delivered to the region of the conventional RPS design in which the plasma is formed will not be uniform and will have a high activity, or “hot spot,” in the regions “PR” (FIG. 1), where the plasma generation device(s) (i.e., coils) are positioned. All of the other portions of the regions 112, 114 will have weak or non-existent power coupling outside of the “PR” regions, due to their distance and position relative the plasma inducing elements (e.g., first and a second cores 104, 106). As schematically illustrated in FIG. 1, conventional RPS designs traditionally use a closed loop RF source configuration that has windings that are wrapped around a closed magnetically permeable core that surrounds a portion of the plasma generating region. The generated fields that are focused by the position and shape of the cores 104, 106 relative to the regions “PR,” have a relatively small area and have a very limited time in which to transfer the RF energy to a gas flowing through the conventional RPS device. Thus, conventional RPS designs that have a small plasma generating region have a very limited ability to generate and/or control the energies of the formed gas radicals and/or gas ions.
To resolve the energy coupling efficiency problems, typically, RPS device manufacturers will generally flow both electro-negative type gases (e.g., ammonia (NH3)) and electro-positive type gases (e.g., argon (Ar)) at the same time through the plasma generation region to more easily form and sustain a generated plasma therein. However, in some cases it is desirable to only deliver a single electro-negative or a single electropositive gas to improve the processing speed or plasma processing results. Also, it is often desirable to form and sustain a plasma within regimes that have a low plasma impedance, such as where the pressure in the plasma generation region is low (e.g., <200 mTorr). Conventional RPS designs that inefficiently couple the plasma energy to the processing gasses are not currently able to meet the needs of the semiconductor processing industry. Therefore, there is a need for an RPS design that more effectively couples the delivered RF energy to the processing gases, has a wider process window and is able to work in a wider range of plasma impedances.
Also, it is typical for conventional RPS designs to utilize a switching power supply to form a plasma in the plasma generation region of the RPS device. The use of switching power supplies is preferred in conventional designs, since they do not require a line isolation circuit or an impedance matching network to deliver the energy to the plasma generation region of the RPS device. Switched-mode power supplies regulate the delivered RF energy by either adjusting the output voltage or current in a pulsed or duty cycle type delivery configuration. However, it has been found that the use of a switching power supply in an RPS design is ineffective in efficiently coupling the delivered RF energy to the plasma. Therefore, there is need to more efficiently couple the delivered RF energy to the gases delivered through the RPS device.
Conventional RPS designs also typically use metal components to enclose the plasma generation region in the RPS device. However, to prevent the attack of the metal components by the RPS energized gases, it is typical to deposit a coating on the surfaces that will be exposed to the plasma and energetic gases. Typically, anodized aluminum coatings have been used on aluminum parts to prevent the attack of the base aluminum surface by the highly energetic species generated in the RPS plasma. However, it has been found that significant process result drift will occur when using coatings in the plasma formation region of an RPS device. The process drift can be created by the interaction of the RPS excited gases with the surfaces of the structural metal components through imperfections in the coating, such as coating porosity or cracks. Coating problems can be especially an issue when the plasma contains oxidizing species or fluorinated species that tend to attack most commonly used metal materials. Therefore, there is a need for an RPS design that avoids the process drift and particle formation due to the attack of the elements that contain the plasma generated in an RPS device.
Also, there is a need in the art for an apparatus and process that more effectively generates and controls the plasma uniformity, and has a larger processing window, without significantly increasing the processing or hardware cost.